Simultaneous dual hand lever control

ABSTRACT

A dual hand lever control for actuating the shipper rod which controls a hydraulic press valve in response to the simultaneous depression of both hand levers. A cross bar, centrally attached to the lower end of the shipper rod, carries a pivotally mounted, bell-crank at each of its opposite ends. Each of these bell cranks is movable with the shipper rod and also is pivotable along a secondary path to permit movement of one of its bellcrank arms into and away from an intermediate position in the path of movement of its cooperating hand lever. A linking bar is pivotally connected at each of its ends to the other bell-crank arm of each bell crank. Actuation of a single control lever exerts a force on its bell crank to pivot the bell crank along its secondary path without moving the shipper rod and, through the linking bar, to withdraw the other bell crank from the path of movement of the hand lever. When both hand levers are operated, these forces are exerted on both bell cranks but are cancelled by the linking bar to permit actuation of the shipper rod.

United States Patent [191 Aslanhayrak et al.

[ Apr. 17, 1973 SIMULTANEOUS DUAL HAND LEVER CONTROL [75] Inventors: Ali R. Aslanbayrak; Ovid W.

Woods, both of Columbus, Ohio [52] US. Cl. ..192/131 R [51] Int. Cl. ..Fl6p 3/22 [58] Field of Search ..192/131 R, 131 H; 91/424, 425

[56] References Cited UNITED STATES PATENTS 3,605,969 9/1971 Comu et al. ..192/131 R 2,171,559 9/1939 Higley ..192/131 R 2,473,167 6/1949 Mills ....l92/13l R X 3,491,867 1/1970 Alexander ..192/131 R FOREIGN PATENTS OR APPLICATIONS 1,067,158 l/l954 France ..192/131 R 1,088,477 9/1954 France ....192/131 R 717,086 2/1942 Germany.... ....l92/l3l R 562,409 5/1957 Italy ..192/131 R Primary Examiner--Allan D. Herrmann Attorney-Anthony D. Cennamo et al.

[57] ABSTRACT A dual hand lever control for actuating the shipper rod which controls a hydraulic press valve in response to the simultaneous depression of both hand levers. A cross bar, centrally attached to the lower end of the shipper rod, carries a pivotally mounted, bell-crank at each of its opposite ends. Each of these bell cranks is movable with the shipper rod and also is pivotable along a secondary path to permit movement of one of its bell-crank arms into and away from an intermediate position in the path of movement of its cooperating hand lever. A linking bar is pivotally connected at each of its ends to the other bell-crank arm of each bell crank. Actuation of a single control lever exerts a force on its bell crank to pivot the bell crank along its secondary path without moving the shipper rod and, through the linking bar, to withdraw the other bell crank from the path of movement of the hand lever. When both hand levers are operated, these forces are exerted on both bell cranks but are cancelled by the linking bar to permit actuation of the shipper rod.

10 Claims, 8 Drawing Figures PATENTED APR 1 71973 SHEET 1 0F 2 INVENTORS ALI RASLANBAYRAK OVID w. WOODS Cumamo .KremL/ufl 5* odlcr ATTORNEYS PMEMEUAP H 3.728.498

SHEET 2 UFZ 700 I20 H2 I24 INVENTORS ALI R. ASLANBAYRAK BY OVID W. WOODS ATTORNEYS SIMULTANEOUS DUAL HAND LEVER CONTROL BACKGROUND OF THE INVENTION This invention relates generally to hand actuated controls and more particularly relates to a mechanical control for actuating a hydraulic valve by the simultaneous depression of a pair of hand levers.

In modern manufacturing plants, many machines and tools are used which are advantageously operated by two hand controls rather than by a control operated by a single hand. One broad class of these mechanisms are the dual hand controls used for actuating hydraulic power presses.

A power press has mating dies, one mounted on the stationary bed of the press and the other mounted on a movable ram which moves with great force toward the press bed. An operator must position a workpiece on the bed die and then actuate the machine to ram the other die upon the workpiece. Some operators of machines which are actuated by a single hand control attempt to feed workpieces into the press with one hand while actuating the press with the other hand.

Unfortunately however, the operators of such machines began to discover that they could tie down or otherwise restrain one of the pair of hand levers in its actuated or an intermediate position and subsequently operate the press as a single hand controlled press.

When operated in the proper and intended manner, the rams of presses equipped with dual hand controls are actuated when both levers of a pair of hand controls are depressed.

There is a need therefore, for a dual hand lever control which actuates a machine when both of its two hand control levers are simultaneously moved from their unactuated to their actuated positions.

SUMMARY OF THE INVENTION The invention is an apparatus for moving a controlled member, which is movably mounted to a support frame, from a deactuated position to an actuated position. The apparatus has a plurality of operating members, such as hand controlled levers, movably mounted to the support frame each movable between a first and a second position. A plurality of actuating members, each biased to a position at which it is engageable with a different one of the operating members, are mounted on the controlled member for movement therewith between said actuated and deactuated positions and for movement relative thereto. A linking means links the actuating members for preventing movement of the actuating members relative to the controlled member upon the substantially, simultaneous engagement of the actuating members by their cooperating operating members when being moved toward their second positions to transmit the operating member movement to said controlled member and move the controlled member to said actuated position. The linking means also moves the actuating members relative to the controlled member upon engagement of fewer than all the actuating members by their cooperating operating members to prevent movement of the controlled member to its actuated position by the substantially nonsimultaneous movement of the operating members toward their second positions.

Accordingly, it is an object of the invention to provide a control for actuating a machine by the simultaneous depression of a pair of hand control levers.

Another object of the invention is to provide for an inexpensive mechanical control having these characteristics. I

Another object of the invention is to provide a simultaneous dual hand control for actuating a valve shipper rod without exerting any bending moment on the shipper rod.

Yet another object of the invention is to provide a simultaneous dual hand control in which the hand levers are returned to their initial unactuated positions prior to recycling of the machine operation.

Further objects and features of the invention will be apparent from the following specification and claims when considered in connection with the accompanying drawings illustrating several embodiments of the invention.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in perspective of a dual hand lever controlled hydraulic press.

FIG. 2 is a diagrammatic view illustrating the operation of the preferred embodiment.

FIG. 3 is a view in perspective of a control apparatus constructed according to the invention.

FIG. 4 is a plan view of the preferred embodiment of the invention illustrated in FIG. 2.

FIG. 5 is a view in side elevation of the embodiment illustrated in FIG. 4.

FIG. 6 is a diagrammatic view of an alternative embodiment of the invention.

FIG. 7 is a diagrammatic view of another alternative embodiment of the invention.

FIG. 8 is a diagrammatic view of another embodiment of the invention.

In describing the preferred embodiments of the invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended to be limited to the specific terms so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

DETAILED DESCRIPTION FIG. 1 illustrates a floor mounted hydraulic press 10 having a generally C-shaped support frame including parallel vertical side panels 18 and 19. A vertically reciprocating ram 12 is mounted above a press-bed or platen 14. The ram 12 is driven downwardly by the piston of a power cylinder 16 mounted to the support frame axially above the ram 12. Mounted between the parallel vertical side panels 18 and 19 of the press 10 and hidden from view are a hydraulic pump, a motor for driving the pump, and a valve for controllably applying the pump pressurized hydraulic fluid to the cylinder 16. These form no part of the present invention. The hydraulic control valve is actuated by a vertically reciprocating, slidable shipper rod 20. In the embodiment illustrated, a sufficient upward movement of the shipper rod 20 slides the valve spool to a position applying hydraulic pressure to the cylinder 16 thereby causing the power descent of the ram 12. The shipper rod 20 is connected by a suitable coupling to the valve spool and is capable of longitudinal movement only, being held against movement of any other nature by means of a slide guide 22.

A pair of manual operating members 24 and 26 ex- -tend from beneath the platen l4 forwardly to a position of accessibility to a standing operator. These operating members 24 and 26 are pivotally mounted in suitable bearings welded transversely through the side panels 18 and 19. When simultaneously depressed the operating members 24 and 26 acting through an intermediate mechanism embodying the present invention raise the shipper arm 20 to actuate the hydraulic control valve. The shoulders 30 and 32, formed by notches in the front flanges 34 and 36 provide suitable stops restricting the downward movement of the operating members 24 and 26.

Referring now to FIGS. 2, 3, 4, and 5, the manual operating member 24 comprises a forwardly extending lever arm 40 having a hand grip 42 at its forward end and an annular ring 44 at its fulcrum which is fixed to a rotatable axle 46 by a set screw 48. It also has a rearwardly extending lever arm 50 fixed to a clamping block 52 which in turn is clamped to the axle 46. The axle 46 is pivotally mounted in a suitable bearing 54 welded transversely in the side panel 18. A tension spring 56 biases the operating member 24 with its forwardly extending hand lever arm 40 in its raised, unactuated position. Similarly, the other manual operating member 26 comprises a forwardly extending lever arm 60 having a handle grip 62 and an annular ring 44 fixed to an axle 66 by a set screw 68. It too has a rearwardly extending lever arm 70 fixed in a clamping block 72 which in turn is clamped on the axle 66. The axle 66 is rotatably mounted in a suitable bearing welded transversely through the opposite side panel 19 illustrated in FIG. 1. The operating member 26 similarly has its forwardly extending lever arm 60 biased in its raised, actuated position by a tension spring 76.

The operating members 24 and 26 rotate in the direction of the movement of the shipper rod 20 and move along paths P and P between a first idle or unactuated position and a second actuated position. That is, the downward movement of the hand grips 42 and 62 produces an upward movement of the rearwardly extending lever arms 50 and 70. As will be seen below, it is a function of the remaining mechanism to transmit this upward movement of the rearwardly extending lever arms 50 and 70 directly to the shipper rod 20 to move the shipper rod 20 vertically upwardly when the forwardly extending lever arms 40 and 60 are simultaneously depressed.

The remaining mechanism is a modified parallelogram linkage which is diagrammatically illustrated in FIG. 2. The base of the parallelogram is rigidly mounted on the shipper rod 20 and comprises a cross bar 80 welded to a mounting block 82 provided with a vertically aligned bore 84. The bore 84 snugly receives the lower end of the shipper rod 20. A roll pin 86 retains the shipper rod in the bore 84 and extends rearwardly through the cross bar 80 and the mounting block 82 and through the lower end of the shipper rod 20.

The opposite ends of the cross bar. 80 extend proximately to the rearwardly extending lever arms 50 and 70 of each operating member 24 and 26. A pair of bell cranks 88 and 90 are pivotally. mounted to each end of the cross bar 80 by means of pins 92 and 94. The bell cranks 88 and 90 form actuating members and have one arm of each, arms 108 and 110, forming opposite lateralsides of the parallelogram linkage. The other bell crank arms 102 and 104 extend downwardly and outwardly and are, at times, engageable with the rearwardly extending lever arms 50 and of the manual operating members 24 and 26. g

A connector bar 106 is the top member of the parallelogram. It is a linking means which is pivotally connected at each end by pins 120 and 122 to theupwardly extending arms 108 and 110 of the bell-cranks 88 and 90.

The bell cranks 88 and 90 being carried on the cross bar move vertically with the shipper rod 20 between its actuated and its deactuated positions. Additionally, they pivot relative to the shipper rod 20 along secondary paths S and S illustrated in FIG. 2. The secondary paths S and S are spaced from the idle positions 50A and 70A of the operating members so that they can never engage an idle manual operating member. The bell cranks 88 and are biased to intermediate positions on their secondary paths by a pair of tension springs 112 and 114. These substantially equal force springs extend from small holes 116 and 118 bored diametrically through the connecting bar pivot pins 120 and 122 to a single pin 124 inserted through a bore in the shipper rod 20. These intermediate positions lie in the paths of movement P and P of the cooperating operating members 24 and 26.

A pair of rearwardly extending bumper assemblies and 132 extend horizontally from the cross bar 80. They have protruding synthetic resin tips 150 and 152 which slide along a vertical plate 134 (FIG. 3) which is a wall of the hydraulic reservoir. The bumper assemblies 130 and 132 have threaded ends 136 and 138 each of which has a pair of nuts 140 and 142, and 144 and 146 which clamp the bumper assemblies 130 and 132 to the cross bar 80 and permit longitudinal adjustment of the bumpers to compensate for any wear in their tips 150 and 152. The bumpers retain the entire parallelgram linkage and the bell cranks against rotation about the shipper rod axis.

Considering now the operation of the preferred control apparatus illustrated in FIGS. l-5, if only one operating member such as the operating member 24 is depressed, then its rearwardly extending lever arm 50 will be raised from its unactuated position 50A into engagement at position 508 with the bell crank 88. The upward movement of the arm 50 against the downwardly extending bell crank arm 104 will apply a force on the bell crank 88 to rotate it in the counterclockwise direction along its secondary path. As the arm 50 is moved further to its position 50C, the bell crank arm 104 will rotate upwardly to the position 104A. At this point, the forwardly extending hand lever arm 40 of the operating member 24 will contact the notched shoulder 30 preventing its further movement.

The moment force applied to the bell crank 88 by the lever arm 50 will be transmitted through the connector bar 106 to the opposite bell crank 90. The bell crank 90 will be pivoted away from its biased intermediate position and be withdrawn from the path of movement P of the rearwardly extending lever arm 70 of the operating member 26. The shipper rod 20 is not moved.

Depression of the other operating member 26 to raise the rearwardly extending lever arm 70 would have no effect on the mechanism because it can not now engage the withdrawn bell crank 90. Release of the actuated operating member 24 will permit the spring 56 to lower the rearwardly extending lever arm 50 and the bell cranks 88 and 90 will be returned along their secondary paths to their biased intermediate positions.

In an alternative modification wherein a fulcrum of each control arm is modified to give a lesser mechanical advantage or the notched shoulders 30 and 32 are lower, and wherein the bell cranks 88 and 90 are modified to permit more angle of rotation, then the rearwardly extending lever arm 50 when actuated, would continue until the bell crank 88 arrived at a position of complete disengagement with the rearwardly extending lever arm 50. The arm 50 would then pass upwardly past the apparatus to position 50D without exerting any further force or causing the upward movement of the shipper rod 20. Both bell cranks would be returned by the springs 112 and 114 to their intermediate positions. Subsequent lowering of the rearwardly extending lever arm 50 would cause it to initially engage the upper cam surface 160 of the bell crank 88. Further lowering of the arm 50 would rotate the bell crank 88 in the opposite direction until the arm 50 passed by and disengaged the bell crank 88 and returned to its unactuated position 50A. Again, the bell cranks 88 and 90 would be returned to their intermediate positions Returning to the illustrated preferred embodiment,

actuation of only the other operating member 26 will cause its rearwardly extending lever arm 70 to move upwardly, engaging and rotating the bell crank 90 in the clockwise direction away from its intermediate position. The opposite bell crank 88 is rotated by the connector bar 106 along its secondary path and thereby withdrawn from the path of movement of the rearwardly extending lever arm 50 of the operating member 24. The shipper rod 20 is not and can not be raised toward its actuated position. The rearwardly extending arm 70 may then be lowered to its initial unactuated position 70A illustrated in FIG. 5 permitting counterclockwise return of the bell cranks 88 and 90 to their intermediate positions.

The above stated sequence of operations would be unchanged if either the rearwardly extending arm 50 or the rearwardly extending arm 70 were maintained in its upper position by tying the operating members 24 or 26 in their actuated positions.

If the operating members 24 and 26 are simultaneously depressed so that the rearwardly extending lever arms 50 and 70 rise and engage both of the cooperating bell cranks 88 and 90 prior to any significant movement of either bell crank away from its intermediate position, then the forces exerted on each bell crank by its cooperating operating member will be resolvable into components in the upward direction of desired movement of the shipper rod and a disengaging component in a direction urging the bell cranks along their secondary paths away from their intermediate positions. The linking connector bar 106, however, will provide counterbalancing of the disengaging forces thereby precluding movement of the bell cranks along their secondary paths and maintaining the bell cranks rigidly in their inter-mediate positions. This permits the lifting component of forces applied to the bell cranks 88 and 90 by the operating members 24 and 26 to lift the shipper arm 20 directly upwardly and thereby actuate the valve and initiate descent of the ram 12.

An alternative embodiment of the invention is diagrammatically illustrated in FIG. 6. The shipper rod 220 has a body 222 rotatably mounted to the bottom end of the shipper rod 220 on an axle 224. A pair of actuating members 226 and 228 are rigidly connected to the body 222 and extend radially therefrom. They are biased into intermediate positions by springs 229 and 231. Upward movement of either operating member 230 or operating member 232 pivots the entire body 222 until the engaged actuating member either completely or nearly disengages the raised operating member. Simultaneously, the other actuating member would be rotated and withdrawn from the path of movement of its cooperating operating member. However, engagement of both operating members 230 and 232 with their cooperating actuating members 226 and 228 permits the body 222 to cancel the moment forces and permits the upward lifting force components of the operating members 30 and 32 to raise the shipper rod 220 to a position of actuation. Illustrated in phantom is the withdrawn position 226A which occurs by the raising of the operating member 232 to its actuated position 232A.

FIG. 7 illustrates diagrammatically yet another embodiment of the invention. This embodiment has a shipper rod 320 connected to a cam member 321 which has a pair of integral, rigidly connected cams 326 and 328. The cams 326 and 328 are slidably mounted in a support frame 330 which is connected to the shipper rod 320 for vertical movement therewith. The cams 326 and 328 can reciprocate laterally and are resiliently biased to an intermediate position by means of a pair of springs 336 and 338. Movable operating members 332 and 334 and biased to the illustrate unactuated positions.

Engagement of a single operating member with its cooperating cam slides the entire cam member 321 away from the engaged operating member. For example, actuation of operating member 332 to position 332A moves the cam member 321 to the position 321A. The singly engaged operating member passes by the cooperating cam member 321 without actuating the shipper rod 320. However, by simultaneously moving operating members 332 and 334 upwardly the shipper rod 320 is moved upwardly because the disengaging forces are cancelled by means of the sliding cam member 321. The upper surfaces 340 and 342 of the cam member 321 are downwardly curved to facilitate the return of a single moved operating member to its unactuated position.

FIG. 8 diagrammatically illustrates still another embodiment of the invention. A shipper rod 420 is welded to a cross bar 480 and has finger-type actuating members 488 and 490 pivotally mounted at each end which cooperate with operating members 424 and 426. The linking means is a tension link such as a cable 406 or a chain. Compression springs 412 and 414 bias the actuating members to an intermediate position in the path of movement of the operating members 424 and 426. Operation of this embodiment is the same as operation of the preferred embodiment illustrated in FIG. 2.

It is to be understood that while the detailed drawings and specific examples given describe the preferred embodiments of the invention, they are for the purposes of illustration only. The apparatus of the invention is' not limited to the precise details and conditions disclosed and various changes may be made therein without departing from the spirit of the invention which is defined by the following claims.

We claim:

1. A control apparatus for moving a controlled member, which is movably mounted to a support frame, from a deactuated position to an actuated position, in response to the substantially simultaneous actuation of a plurality of operating members, said apparatus comprising:

a. a plurality of operating members mounted on said frame, each operating member movable along a path between a first and a second position;

. a plurality of actuating members each cooperating with a different operating member and mounted on the controlled member for movement therewith between said actuated position and said deactuated position, each actuating member also movable relative to the controlled member along a secondary path which is spaced from the first position of its cooperating operating member for preventing engagement of the actuating member with its operating member when in the first position, each of the actuating members being biased to an intermediate position on its secondary path, said intermediate position being in the path of movement of its cooperating operating member to permit engagement of each actuating member by its cooperating, operating member when the operating member is moved toward its second position and for exerting a force urging movement of an engaged actuating member along only its secondary path without moving the controlled member when fewer than all operating members engage their cooperating actuating members;

linking means interconnecting said actuating members for counterbalancing each of said forces when all of said operating members simultaneously engage their cooperating actuating members to rigidly maintain the actuating members in their intermediate positions precluding movement along their secondary paths and to permit movement of the controlled member and the actuating members toward said actuated position in response to the substantially simultaneous movement of all said operating members toward their second position.

2. An apparatus according to claim 1 wherein said actuating members comprise a pair of rigidly connected cams having tapered end surfaces which are resiliently biased into said intermediate position and slidably mounted on the controlled member for longitudinal reciprocation.

3. An apparatus according to claim 1 wherein there are a pair of cooperating operating members and actuating members and wherein said linking means withdraws one actuating member out of the path of movement of its cooperating member when the other actuating member is moved along its secondary path by the other operating member.

4. A con rol apparatus according to claim 3 wherein each of said actuating members comprises an arm pivotally mounted on said controlled member and said linking means comprises a tension link connected at each end to said arms.

5. An apparatus according to claim 3 wherein saidactuating members comprise a body rotatably mounted to said controlled member and having a pair of arms extending rigidly therefrom and resiliently biased into said intermediate position.

6. An apparatus according to claim 3 wherein the operating members comprise a pair of manual control levers pivotally mounted to said frame; said actuating members comprise a pair of bell-cranks pivotally mounted to said controlled member having one arm of each bell-crank engageable with a different operating member and having the other arm of each bell crank connected to said linking means.

7. A control apparatus according to claim 6 wherein the linking means comprises a connector bar pivotally connected at each end to said other arms of said actuating members.

8. A control apparatus according to claim 7 wherein a cross bar is rigidly mounted to said controlled member and said bell-cranks are pivotally mounted to opposite ends of said cross bar.

9. A control apparatus according to claim 8 wherein the engageable bell-crank arms extend generally outwardly and downwardly from the ends of said cross bar.

10. A control according to claim 9 wherein the sup port frame includes a hydraulic press and said controlled member is a valve actuating shipper rod; wherein said control levers are resiliently biased upwardly to an unactuated position and include hand grips extending outwardly to be accessible to an operatOl'. 

1. A control apparatus for moving a controlled member, which is movably mounted to a support frame, from a deactuated position to an actuated position, in response to the substantially simultaneous actuation of a plurality of operating members, said apparatus comprising: a. a plurality of operating members mounted on said frame, each operating member movable along a path between a first and a second position; b. a plurality of actuating members each cooperating with a different operating member and mounted on the controlled member for movement therewith between said actuated position and said deactuated position, each actuating member also movable relative to the controlled member along a secondary path which is spaced from the first position of its cooperating operating member for preventing engagement of the actuating member with its operating member when in the first position, each of the actuating members being biased to an intermediate position on its secondary path, said intermediate position being in the path of movement of its cooperating operating member to permit engagement of each actuating member by its cooperating, operating member when the operating member is moved toward its second position and for exerting a force urging movement of an engaged actuating member along only its secondary path without moving the controlled member when fewer than all operating members engage their cooperating actuating members; c. linking means interconnecting said actuating members for counterbalancing each of said forces when all of said operating members simultaneously engage their cooperating actuating members to rigidly maintain the actuating members in their intermediate positions precluding movement along their secondary paths and to permit movement of the controlled member and the actuating members toward said actuated position in response to the substantially simultaneous movement of all said operating members toward their second position.
 2. An apparatus according to claim 1 wherein said actuating members comprise a pair of rigidly connected cams having tapered end surfaces which are resiliently biased into said intermediate position and slidably mounted on the controlled member for longitudinal reciprocation.
 3. An apparatus according to claim 1 wherein there are a pair of cooperating operating members and actuatinG members and wherein said linking means withdraws one actuating member out of the path of movement of its cooperating member when the other actuating member is moved along its secondary path by the other operating member.
 4. A control apparatus according to claim 3 wherein each of said actuating members comprises an arm pivotally mounted on said controlled member and said linking means comprises a tension link connected at each end to said arms.
 5. An apparatus according to claim 3 wherein said actuating members comprise a body rotatably mounted to said controlled member and having a pair of arms extending rigidly therefrom and resiliently biased into said intermediate position.
 6. An apparatus according to claim 3 wherein the operating members comprise a pair of manual control levers pivotally mounted to said frame; said actuating members comprise a pair of bell-cranks pivotally mounted to said controlled member having one arm of each bell-crank engageable with a different operating member and having the other arm of each bell crank connected to said linking means.
 7. A control apparatus according to claim 6 wherein the linking means comprises a connector bar pivotally connected at each end to said other arms of said actuating members.
 8. A control apparatus according to claim 7 wherein a cross bar is rigidly mounted to said controlled member and said bell-cranks are pivotally mounted to opposite ends of said cross bar.
 9. A control apparatus according to claim 8 wherein the engageable bell-crank arms extend generally outwardly and downwardly from the ends of said cross bar.
 10. A control according to claim 9 wherein the support frame includes a hydraulic press and said controlled member is a valve actuating shipper rod; wherein said control levers are resiliently biased upwardly to an unactuated position and include hand grips extending outwardly to be accessible to an operator. 